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oligodendrocyte

(ol″ĭ-gō-den′drŏ-sīt″) [oligo- + dendro- + -ocyte] A glial cell that is found most commonly in axon tracts and myelinates axons in the central nervous system just as Schwann cells myelinate axons in the peripheral nervous system. Oligodendrocytes are neuroectodermal cells that originate from different precursors in the neural tube than astrocytes; later, stem cells in the subependymal layer can continue to generate new oligodendrocytes. Mature oligodendrocytes wrap neighboring axons in myelin, and some oligodendrocytes can simultaneously wrap many axons. However, not all oligodendrocytes myelinate axons. SYN: olfactory cell; oligodendroglia. SEE: glial cell; illus.

oligogenic

oligohydramnios

(ŏl″ĭg-ō-hī-drăm′nē-ōs) [″ + hydor, water, + amnion, amnion] An abnormally small amount of amniotic fluid. It is a rare condition in which the volume of amniotic fluid during the third trimester is less than 300 ml. Insufficient fluid surrounding the fetus increases the potential for cord compression, fetal hypoxia, fetal malformation, perinatal demise, and dysfunctional and prolonged labor. Although the etiology is unknown, the disorder is associated with amniotic fluid leakage, placental insufficiency, post-maturity, intrauterine growth retardation, and major congenital abnormalities of the fetal kidney or lungs.